Fully differential variable gain instrumentation amplifier based on a fully differential DDA topology

A fully Differential Instrumentation Amplifier (DIA) based on a two-stage Fully differential Differential Difference Amplifier (FDDA) cell is presented. The overall topology of this FDDA is described, referring to the input linear transconductance ports and the open-loop characteristics of the two-stage amplifier. Based on this fully differential analogue cell, a new variable gain fully differential instrumentation amplifier is proposed. This new topology is based on the FDDA cell, with a voltage-controlled differential linear transconductance cell used in the feedback loop of the amplifier to control the amplifier´s gain, The gains can be continuously tuned within each gain decade variation range by a controlling voltage V_g. Two equal feedback resistors set the gain variation decade, allowing gains between 15 and 60 dB. Simulation results of the developed structure are presented and discussed and some applications of these analogue building blocks are referred to